There are no errors and ive tested in studio and it doesnt work?

it doesnt work , some already fixed the older version of the script.

	local ItemSlot1 = script.Parent.Parent.Parent.ItemSlot1
	local ItemSlot2 = script.Parent.Parent.Parent.ItemSlot2
	local ItemSlot3 = script.Parent.Parent.Parent.ItemSlot3
	 
	local EquipedSlots1 = script.Parent.Parent.Parent.EquipedSlots1
	local EquipedSlots2 = script.Parent.Parent.Parent.EquipedSlots2
	local EquipedSlots3 = script.Parent.Parent.Parent.EquipedSlots3
	 
	script.Parent.MouseButton1Click:Connect(function()
	    if ItemSlot1.Value == false then
	        script.Parent.Visible = false
	        EquipedSlots1.Visible = true
	        ItemSlot1.Value = true
	return ;
	end
	 
	        if ItemSlot2.Value == false then
	            script.Parent.Visible = false
	            EquipedSlots2.Visible = true
	            ItemSlot2.Value = true
	return ;
	end
	 
	            if ItemSlot3.Value == false then
	                script.Parent.Visible = false
	                EquipedSlots3.Visible = true
	                ItemSlot3.Value = true
	                elseif ItemSlot3.Value == true then
	                    print("All slots are being used.")
	         end
	 
	end)

Improvements

Use local variables for all instances which are used more than once as it makes your code easier to read and edit

Use :WaitForChild() to make sure an instance exists before using it (if it doesn't exist, you will see an infinite yield in the Output telling you so)

Use elseif in conjunction with your initial if statement instead of multiple if-then. When the first condition is not met, the next condition will be tested.

Use .Activated() so that your code works for all devices and not just computers.

Potential Issues

Parenting may be incorrect, the WaitForChild will help you determine if this is the case, so you'd need to alter the reference of the local variable

If this is a Server Script, only LocalScripts will work for Text/Image Buttons, so youd need to change the script type.

Issues

In ROBLOX Lua, you do not require a semicolon after the return, (which you'd need for Java).

Revised Local Script

local button = script.Parent
local folder = button.Parent.Parent
local ItemSlot1 = folder:WaitForChild("ItemSlot1")
local ItemSlot2 = folder:WaitForChild("ItemSlot2")
local ItemSlot3 = folder:WaitForChild("ItemSlot3")
local EquipedSlots1 = folder:WaitForChild("EquipedSlots1")
local EquipedSlots2 = folder:WaitForChild("EquipedSlots2")
local EquipedSlots3 = folder:WaitForChild("EquipedSlots3")

button.Activated:Connect(function()
	if ItemSlot1.Value == false then
		button.Visible = false
		EquipedSlots1.Visible = true
		ItemSlot1.Value = true
	elseif ItemSlot2.Value == false then
		button.Visible = false
		EquipedSlots2.Visible = true
		ItemSlot2.Value = true
	elseif ItemSlot3.Value == false then
		button.Visible = false
		EquipedSlots3.Visible = true
		ItemSlot3.Value = true
	else
		print("All slots are being used.")
	end
end)